Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 31-03-2014, 07:54   #1
Registered User

Join Date: Apr 2011
Location: Northport, Michigan
Boat: Trailerable cruising boat
Posts: 301
DSC Distress Message Test

I recently tested an older VHF Marine Band radio qualified to RTCM SC-101 by transmitting (into a dummy load) a DSC distress message. During the test I found:

--the interface of the radio to a GPS receiver was unnecessarily complicated;

--my initial, unrehearsed attempt to send a DSC distress message failed due to operator error; and

--the position data sent by the older radio was limited in resolution.

I describe the test in detail at

continuousWave: Whaler: Reference: DSC Distress Test

and hope that it might be of interest to some readers.
__________________

__________________
continuouswave is offline   Reply With Quote
Old 31-03-2014, 13:30   #2
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2006
Location: Chesapeake Region and Maine
Boat: 42' Bob Perry sloop
Posts: 4,038
Images: 4
Re: DSC Distress Message Test

James,

Thanks for doing this and reporting on the tests. The writeup was excellent: detailed, lucid, and most informative.

Bill
WA6CCA
__________________

__________________
btrayfors is offline   Reply With Quote
Old 31-03-2014, 14:24   #3
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: DSC Distress Message Test

I don't think sc101 is allowed for sale anymore in the US. It was never allowed internationally

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 31-03-2014, 15:10   #4
Registered User

Join Date: Apr 2011
Location: Northport, Michigan
Boat: Trailerable cruising boat
Posts: 301
Re: DSC Distress Message Test

The FCC required VHF Marine Radios sold in the USA to conform at least the RTCM SC-101 recommendation after June, 1999, and permitted them to be sold until March, 2011. That is a period of over ten years, and I expect there are plenty of them in service still.

I don't know for a fact that the USA was the only nation to permit RTCM SC-101 DSC radios, but I have heard that mentioned.
__________________
continuouswave is offline   Reply With Quote
Old 31-03-2014, 18:14   #5
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: DSC Distress Message Test

Quote:
Originally Posted by continuouswave View Post
The FCC required VHF Marine Radios sold in the USA to conform at least the RTCM SC-101 recommendation after June, 1999, and permitted them to be sold until March, 2011. That is a period of over ten years, and I expect there are plenty of them in service still.

I don't know for a fact that the USA was the only nation to permit RTCM SC-101 DSC radios, but I have heard that mentioned.

Well unlike the ITU. RTCM is a purely national body

Dave


Sent from my iPad using Tapatalk
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 31-03-2014, 21:12   #6
Registered User

Join Date: Apr 2011
Location: Northport, Michigan
Boat: Trailerable cruising boat
Posts: 301
Re: DSC Distress Message Test

Quote:
Originally Posted by goboatingnow View Post
Well unlike the ITU. RTCM is a purely national body....
From the website of the RTCM:

"The Radio Technical Commission for Maritime Services (RTCM) is an international non-profit scientific, professional and educational organization. RTCM members are organizations (not individuals) that are both non-government and government. Although started in 1947 as a U.S. government advisory committee, RTCM is now an independent organization supported by its members from all over the world."

The Radio Technical Commission for Maritime Services

But that is not the point of my test. There are plenty of these older DSC radios in use. I tested one, and found the results interesting. Given the low cost of a new Class-D qualified DSC radio, now selling for under $100, it seems crazy not to upgrade.
__________________
continuouswave is offline   Reply With Quote
Old 01-04-2014, 04:12   #7
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
DSC Distress Message Test

Quote:
Originally Posted by continuouswave View Post
From the website of the RTCM:

"The Radio Technical Commission for Maritime Services (RTCM) is an international non-profit scientific, professional and educational organization. RTCM members are organizations (not individuals) that are both non-government and government. Although started in 1947 as a U.S. government advisory committee, RTCM is now an independent organization supported by its members from all over the world."

The Radio Technical Commission for Maritime Services

But that is not the point of my test. There are plenty of these older DSC radios in use. I tested one, and found the results interesting. Given the low cost of a new Class-D qualified DSC radio, now selling for under $100, it seems crazy not to upgrade.

In practice, there is very little user difference between SC101 and class D, the lack of a dedicated DSC receiver is in most cases not apparent to the user.

What you do see, is that in early DSC radios , is inconsistent software. Often the regulations and operations procedures were mis understood or the ground was shifting under the radio manufacturers as the ITU updated the specs. ICOM was a classic case early on, with all sorts of mix up of features, funny nomenclature etc.

Today most of that is ironed out. The single biggest innovation being the integrating of GPS into the radio as Un designated distress alerts with invalid location is a very common event

In my view DSC was overly complicated by merging the desire to remove listening watches on bridges and the distress alerting feature(s)

Furthermore GMDSS was designed with the assumption that the radio operator has received formal training, in several notable countries that is not the case and the misunderstandings that have been generated are leading to views that the system is too complex and prone to false alerts.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 01-04-2014, 05:46   #8
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2006
Location: Chesapeake Region and Maine
Boat: 42' Bob Perry sloop
Posts: 4,038
Images: 4
Re: DSC Distress Message Test

Quote:
Originally Posted by goboatingnow View Post
...........

In my view DSC was overly complicated by merging the desire to remove listening watches on bridges and the distress alerting feature(s) .....

.........the misunderstandings that have been generated are leading to views that the system is too complex and prone to false alerts.

Dave
You think?

Even very experienced boaters and trained radio folks don't fully understand DSC operations .... even the VHF variety, much less HF/DSC.

IMHO, that's led not only to mistakes and false alerts but to the very slow adoption of DSC use even 10 years after it's mandatory introduction on marine radios.

Bill
__________________
btrayfors is offline   Reply With Quote
Old 01-04-2014, 06:34   #9
Registered User

Join Date: Apr 2007
Posts: 718
Re: DSC Distress Message Test

It's the idiot factor. Idiots, nitwits, morons, sheeple, whatever you like to call them. The Coast Guard is receiving approximately 100 DSC distress calls per month. 90% of them have no position information and 60% have unregistered ID numbers. That means the idiots are programming their radio's with random numbers or entered their number wrong because they won't transmit DSC at all without a number. Ah, the ever increasing dumbing down of American society

Eric
__________________
fairbank56 is offline   Reply With Quote
Old 01-04-2014, 06:43   #10
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2006
Location: Chesapeake Region and Maine
Boat: 42' Bob Perry sloop
Posts: 4,038
Images: 4
Re: DSC Distress Message Test

Eric,

I agree with you...that's about half the problem. Take the dumbed down boating public (some of whom have never even seen a nautical chart) and mix that with a VERY COMPLEX digital system and you get what you get.

For those who think it's not complicated, I invite you to peruse the 39 pages of instructions on DSC use in the Icom M802 manual. Read carefully, 'cause there will be a test :-)

Bill
__________________
btrayfors is offline   Reply With Quote
Old 01-04-2014, 08:18   #11
Registered User

Join Date: Apr 2011
Location: Northport, Michigan
Boat: Trailerable cruising boat
Posts: 301
Re: DSC Distress Message Test

Quote:
Originally Posted by goboatingnow View Post
In practice, there is very little user difference between SC101 and class D, the lack of a dedicated DSC receiver is in most cases not apparent to the user.
I agree and disagree.

From a formal standards view, the differences are modest. But based on typical implementation of the standards into real radios, the differences are significant.

Foremost perhaps is the mandate in Class-D to support the enhanced position resolution data. A close second is the much better user interface that is typically found. A simple-to-operate user interface which can be learned in ten minutes is required.

Although not mentioned in my test (because the test focuses on sending a DSC message), I discovered that the RTCM SC-101 radio under test permitted the operator to completely disable its receiver monitoring of Channel-70 for DSC calls. As it turned out, the radio I tested had been set to have DSC WATCH set to OFF, making it completely deaf to any DSC call. Turning DSC WATCH to ON required careful study of the manual and use of a special escape sequence at power-on to access a hidden settings menu.
__________________
continuouswave is offline   Reply With Quote
Old 01-04-2014, 18:09   #12
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: DSC Distress Message Test

Quote:
Originally Posted by continuouswave View Post
I agree and disagree.



From a formal standards view, the differences are modest. But based on typical implementation of the standards into real radios, the differences are significant.



Foremost perhaps is the mandate in Class-D to support the enhanced position resolution data. A close second is the much better user interface that is typically found. A simple-to-operate user interface which can be learned in ten minutes is required.



Although not mentioned in my test (because the test focuses on sending a DSC message), I discovered that the RTCM SC-101 radio under test permitted the operator to completely disable its receiver monitoring of Channel-70 for DSC calls. As it turned out, the radio I tested had been set to have DSC WATCH set to OFF, making it completely deaf to any DSC call. Turning DSC WATCH to ON required careful study of the manual and use of a special escape sequence at power-on to access a hidden settings menu.

Standard horizon class D VHF can be set to disable DSC completely.

The DSC packet is the same for SC101 as it is for class D. It's an implementation feature of that radio in relation to position resolution , the same is true for the user interface.

Dave


Sent from my iPad using Tapatalk
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 01-04-2014, 18:11   #13
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: DSC Distress Message Test

Quote:
Originally Posted by btrayfors View Post
You think?

Even very experienced boaters and trained radio folks don't fully understand DSC operations .... even the VHF variety, much less HF/DSC.

IMHO, that's led not only to mistakes and false alerts but to the very slow adoption of DSC use even 10 years after it's mandatory introduction on marine radios.

Bill

I'm a former VHF GMDSS CEPT license instructor. It's not difficult to get people through the training course. I've had 15 year olds and grannies successfully do it. The main problem is lack of practice as DSC get so little used.

DSC is used a lot to contact ships round here

Dave


Sent from my iPad using Tapatalk
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 01-04-2014, 23:01   #14
Registered User

Join Date: Apr 2011
Location: Northport, Michigan
Boat: Trailerable cruising boat
Posts: 301
Re: DSC Distress Message Test

Quote:
Originally Posted by goboatingnow View Post
The DSC packet is the same for SC101 as it is for class D.
Yes, the DSC packet is the same, but the Class-D radio then sends enhanced position data, so the outcome is completely different. I am more interested in discussing the outcome than in discussing the minutia of the protocols. If I send a position report or a distress message with an SC-101 radio it only has a resolution of one nautical mile. If I send it with a Class-D radio it can have a resolution of six-inches. That is a significant difference. I really don't care too much if the radio has to send an extra packet to get the different outcome.

Do you?
__________________
continuouswave is offline   Reply With Quote
Old 01-04-2014, 23:10   #15
Registered User

Join Date: Apr 2011
Location: Northport, Michigan
Boat: Trailerable cruising boat
Posts: 301
Re: DSC Distress Message Test

Quote:
Originally Posted by goboatingnow View Post
Standard horizon class D VHF can be set to disable DSC completely...
Could you point to the page of the manual for the Standard-Horizon GX1500S radio, a Class-D DSC radio made by Standard-Horizon, where the DSC functions can be completely disabled. I reviewed the owner's manual carefully trying to find that option, but I could not. Other than not assigning an MMSI to the radio, I don't see where you completely shut off the DSC functions.
__________________

__________________
continuouswave is offline   Reply With Quote
Reply

Tags
distress, dsc

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Icom M-802 Instr Videos(basic-adv) & LIVE DSC-Distress Call ka4wja Marine Electronics 49 08-05-2017 08:37
What Is A "Relay" Distress Alert On MY VHF DSC? SecondWind90814 Marine Electronics 11 15-02-2014 05:18
DSC Calling for Other than Distress ? SvenG Marine Electronics 24 23-10-2010 12:45



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 11:43.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.